JP2013161731A - Sealed lithium secondary battery - Google Patents

Abstract

Provided is a sealed lithium secondary battery having a current interruption mechanism, which can improve the reliability as compared with the related art.
According to the present invention, a sealed lithium secondary battery 100 in which an electrode body 80 and an electrolyte are accommodated in a predetermined battery case is provided. The sealed lithium secondary battery 100 includes an additive that generates a gas when a predetermined battery voltage is exceeded, and a current blocking mechanism 30 that operates when the internal pressure of the battery case increases due to the generation of the gas. I have. Here, the electrode body 80 has a structure in which the positive electrode 10 and the negative electrode 20 face each other via two or more separators 40 (or 42) that are independent and overlapped with each other.
[Selection] Figure 2

Description

  The present invention relates to a sealed lithium secondary battery (typically a sealed lithium ion battery). Specifically, the present invention relates to a sealed lithium secondary battery provided with a current interrupting mechanism that operates by increasing internal pressure.

  Lithium ion batteries and other lithium secondary batteries are smaller, lighter and have a higher energy density than the existing batteries, and are excellent in output density. For this reason, in recent years, it is preferably used as a so-called portable power source for personal computers and portable terminals, and a power source for driving vehicles.

  One form of such a battery is a sealed lithium secondary battery. The battery is typically mounted with a lid after an electrode body composed of positive and negative electrodes having a composite layer containing an active material is housed in a battery case together with an electrolyte (typically, an electrolyte). It is constructed by being sealed (sealed). Sealed lithium secondary batteries are generally used in a state where the voltage is controlled so as to be within a predetermined region (for example, 3.0 V or more and 4.2 V or less). As a result, overcharging may occur beyond a predetermined voltage.

  As an overcharge countermeasure technique, a current interruption device (CID; Current Interrupt Device) that cuts off a charging current when the pressure in the battery case reaches a predetermined value or more is widely used. In general, when a battery is overcharged, a nonaqueous solvent or the like of the electrolytic solution is electrolyzed to generate gas. The current interruption mechanism can prevent further overcharging by cutting the charging path of the battery based on the gas generation.

When such a current interruption mechanism is used, a compound (hereinafter referred to as “overcharge inhibitor”) having an oxidation potential lower than that of the non-aqueous solvent of the electrolytic solution (that is, a voltage at which the oxidative decomposition reaction is low) is reduced in advance. There is known a method of containing it in an electrolytic solution. When the battery is overcharged, the overcharge inhibitor is rapidly oxidized and decomposed on the surface of the positive electrode (typically, the positive electrode active material or the conductive material in the positive electrode mixture layer) to generate hydrogen ions (H ⁺ ). . The hydrogen ions diffuse and are reduced on the negative electrode to generate hydrogen gas (H ₂ ). Since the internal pressure of the battery rises due to the generation of such hydrogen gas, the current interruption mechanism can be operated quickly. As this type of prior art, for example, Patent Document 1 discloses a technique using cyclohexylbenzene (CHB) or biphenyl (BP) as an overcharge inhibitor.

JP 2006-324235 A

  However, in such a lithium secondary battery, in particular, when the use environment and / or the storage environment is a high temperature (for example, 50 to 60 ° C.), the viscosity of the electrolyte solution is reduced, and the redox shuttle reaction of the overcharge inhibitor occurs. Preferentially occurs. For this reason, the decomposition reaction of the overcharge inhibitor is suppressed, and there is a risk that the amount of hydrogen gas required to operate the current interruption mechanism may be reduced.

  The present invention has been made in view of the above points, and an object of the present invention is a sealed lithium secondary battery provided with a current interruption mechanism that operates due to an increase in pressure in a battery case, and has improved reliability as compared with the prior art. The battery is provided.

In order to achieve the above object, a sealed lithium secondary battery in which an electrode body and an electrolyte are accommodated in a predetermined battery case is provided. The sealed lithium secondary battery includes an additive that generates a gas when a predetermined battery voltage is exceeded, and a current interruption mechanism that operates when the internal pressure of the battery case increases due to the generation of the gas. ing. Here, the electrode body has a structure in which a positive electrode and a negative electrode are opposed to each other through two or more separators that are independent and overlapped with each other.
In the battery described above, an interface exists between the separators / separators by overlapping a plurality of mutually independent separators. For this reason, the movement of the cation radical generated at the positive electrode can be inhibited at the interface, and the amount of the cation radical reaching the negative electrode surface can be suppressed as compared with the conventional case. Therefore, even when the battery environment becomes high temperature and the viscosity of the electrolytic solution decreases, the redox shuttle reaction of the overcharge inhibitor can be suppressed. Moreover, since the decomposition reaction of the overcharge inhibitor is promoted by suppressing the redox shuttle reaction, the amount of gas generated at the time of overcharge can be increased compared to the conventional case. Therefore, the internal pressure increase necessary for operating the current interrupt mechanism can be stably generated at an early stage.

As a preferred embodiment of the sealed lithium secondary battery disclosed herein, the electrode body is formed on a predetermined positive electrode current collector and two or more long separators independent of each other. A positive electrode mixture layer having a predetermined width is formed on a long positive electrode layer in which a positive electrode mixture layer having a width is formed along the longitudinal direction of the current collector and the long negative electrode current collector. A long negative electrode formed along the longitudinal direction of the current collector, and the long positive electrode and the long negative electrode are opposed to each other through the two or more separators And a wound electrode body that is laminated and wound in the longitudinal direction.
Since a battery equipped with a wound electrode body has a high capacity among lithium secondary batteries, it is particularly important to improve reliability (for example, measures against malfunctions). According to the technology disclosed herein, the reliability (for example, resistance to overcharge and internal short circuit) of such a battery can be improved as compared with the conventional technology.

As a preferred embodiment of the sealed lithium secondary battery disclosed herein, at least one of the separators includes a porous heat-resistant layer containing an inorganic filler on one surface of the separator.
The separator provided with the porous heat-resistant layer can further increase the interface between the separators because the specific surface area of the porous heat-resistant layer is large. Moreover, since it is excellent in heat resistance, the application effect of the present invention (that is, an increase in the amount of gas generated under a high temperature environment) can be further exhibited. Furthermore, in the above battery comprising a separator with a porous heat-resistant layer, heat generation due to internal short circuit is suppressed even when the battery is deformed by impact such as dropping, or when it is destroyed by nail penetration of a metal object. can do. Therefore, the reliability (resistance to overcharge and internal short circuit) of the battery can be improved compared to the conventional case.

As a preferred embodiment of the sealed lithium secondary battery disclosed herein, two or more separators including the separator having the porous heat-resistant layer are arranged in a state where the porous heat-resistant layer is sandwiched between the separators. It is mentioned that.
By disposing the porous heat-resistant layer between the separators, the interface between the separators necessary for inhibiting the movement of the cation radical can be further increased. Therefore, since the decomposition reaction of the overcharge inhibitor necessary for operating the current interruption mechanism can be further promoted, the application effect of the present invention can be further exhibited.

As a preferred embodiment of the sealed lithium secondary battery disclosed herein, the inorganic filler contains at least one selected from the group consisting of alumina, magnesia, zirconia, silica, boehmite, and titania. Is mentioned.
The inorganic compound has a high melting point and is excellent in heat resistance and chemical stability, and therefore can be preferably used.

As a preferred embodiment of the sealed lithium secondary battery disclosed herein, the total thickness of the two or more separators is 5 μm or more and 70 μm or less.
According to such a configuration, even when a plurality of separators are provided as in the present invention, the resistance (typical) associated with such charging / discharging is not significantly reduced without significantly reducing the mobility of lithium ions required for charging / discharging. Therefore, the charge transfer resistance can be kept low. Therefore, it is possible to increase the reliability of the battery (for example, resistance to overcharge and internal short circuit) while maintaining excellent battery performance.

As a preferred embodiment of the sealed lithium secondary battery disclosed herein, the porosity of the whole of the two or more separators is 30% by volume to 80% by volume.
When satisfy | filling the said porosity, the fall of the battery performance (for example, the fall of battery capacity or cycling characteristics) resulting from providing a plurality of separators can be suppressed further. Therefore, the battery performance and the improvement of the battery reliability (for example, resistance to overcharge and internal short circuit) can be achieved at a high level.

A preferred embodiment of the sealed lithium secondary battery disclosed herein includes cyclohexylbenzene or biphenyl as the additive (overcharge preventing agent).
Cyclohexylbenzene and biphenyl have a relatively low oxidation potential of 4.5 to 4.6 V and can be rapidly oxidized and decomposed to generate hydrogen gas during overcharge. For this reason, a current interruption mechanism can be operated more rapidly.

As a preferred embodiment of the sealed lithium secondary battery disclosed herein, the additive is added in an amount of 0.5% by mass to 5% by mass with respect to 100% by mass of the electrolyte.
In the technology disclosed here, since the reaction efficiency of the overcharge inhibitor is high, the amount of gas necessary for reliably operating the current interrupting device at a high temperature can be reduced with a small amount of overcharge inhibitor compared to the conventional technology. Can be obtained.

  Further, there is provided a vehicle including the sealed lithium secondary battery disclosed herein as a driving power source. Such a sealed lithium secondary battery is characterized in that the reliability during overcharge is improved even in a high temperature environment. For this reason, it is particularly effective when the battery has a high capacity and a high output and can be used and / or left in a high temperature. For example, a vehicle (typically, a plug-in hybrid vehicle (PHV), a hybrid, etc. It can be suitably used as a power source (drive power source) for driving a motor mounted on an automobile (HV) or an electric vehicle (EV).

1 is a perspective view schematically showing an outer shape of a sealed lithium secondary battery according to an embodiment of the present invention. It is a figure which shows typically the cross-sectional structure in the II-II line | wire of the sealed lithium secondary battery of FIG. It is a schematic diagram which shows the structure of the winding electrode body of the sealed lithium secondary battery based on one Embodiment of this invention. It is a side view which shows the vehicle (automobile) provided with the sealed lithium secondary battery based on one Embodiment of this invention. It is typical sectional drawing which shows the structure of the sealed lithium secondary battery based on one Example of this invention, (A)-(D) each differ in the aspect of a separator.

In the present specification, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged / discharged by movement of charges accompanying the lithium ions between the positive and negative electrodes. A secondary battery generally referred to as a lithium ion battery (or lithium ion secondary battery) is a typical example included in the lithium secondary battery in this specification. Further, in this specification, the “active material” refers to a substance (compound) involved in power storage on the positive electrode side or the negative electrode side. That is, it refers to a substance that is involved in the insertion and extraction of electrons during battery charge / discharge.
In the present specification, the overcharge state refers to a state in which the charge depth (SOC) exceeds 100%. The SOC is a charge state (that is, a fully charged state) in which an upper limit voltage is obtained in an operating voltage range that can be reversibly charged and discharged, and a charge state (that is, a lower limit voltage is obtained). , The state of not being charged) shows the state of charge when 0%.

  Hereinafter, preferred embodiments of the sealed lithium secondary battery disclosed herein will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for implementation can be grasped as design matters of those skilled in the art based on the prior art in this field. The sealed lithium secondary battery having such a structure can be implemented based on the contents disclosed in the present specification and common technical knowledge in the field.

As the positive electrode of the lithium secondary battery disclosed herein, a positive electrode active material, a conductive material, a binder (binder), etc. are mixed in a suitable solvent to include a slurry (paste or ink). The composition (hereinafter referred to as “positive electrode mixture slurry”) was prepared, and the slurry was applied onto the positive electrode current collector to form a positive electrode mixture layer (also referred to as a positive electrode active material layer). Use the form.
Examples of the material for the positive electrode current collector include aluminum, nickel, titanium, and stainless steel. The shape of the current collector is not particularly limited because it can vary depending on the shape of the battery to be constructed, and a rod-like body, a plate-like body, a foil-like body, a net-like body, or the like can be used. In addition, in the battery provided with the winding electrode body mentioned later, a foil-like body is mainly used. The thickness of the foil-shaped current collector is not particularly limited, but about 5 μm to 50 μm (more preferably 8 μm to 30 μm) can be preferably used in consideration of the capacity density of the battery and the strength of the current collector.

As the positive electrode active material, one type or two or more types of materials conventionally used in lithium secondary batteries can be used without any particular limitation. For example, an oxide containing lithium and a transition metal element as constituent metal elements such as lithium nickel oxide (eg LiNiO ₂ ), lithium cobalt oxide (eg LiCoO ₂ ), lithium manganese oxide (eg LiMn ₂ O ₄ ) Examples thereof include lithium transition metal oxides), phosphates including lithium and transition metal elements such as lithium manganese phosphate (LiMnPO ₄ ) and lithium iron phosphate (LiFePO ₄ ) as constituent metal elements. Among them, a positive electrode active material (typically substantially lithium nickel cobalt manganese) having a layered structure lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) as a main component. A positive electrode active material made of a composite oxide is preferably used because of its excellent thermal stability and high energy density. Although not particularly limited, the proportion of the positive electrode active material in the entire positive electrode mixture layer is 50% by mass or more (typically 70% by mass or more and 100% by mass or less, for example, 80% by mass or more and 99% by mass or less). It is preferable that

Here, the lithium nickel cobalt manganese composite oxide is an oxide having Li, Ni, Co, and Mn as constituent metal elements, and at least one other metal element (Li, Ni, Co, and Mn) in addition to Li, Ni, Co, and Mn. The meaning also includes oxides containing transition metal elements and / or typical metal elements other than Ni, Co, and Mn. Such metal elements are, for example, one or more elements of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. It can be. The same applies to lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide. As such a lithium transition metal oxide (typically in particulate form), for example, a lithium transition metal oxide powder prepared by a conventionally known method can be used as it is. Although not particularly limited, for example, the D ₅₀ particle size is substantially constituted by secondary particles in the range of about 1 μm to 25 μm (preferably 2 μm to 10 μm, more preferably 6 μm to 10 μm, for example 6 μm to 8 μm). The obtained lithium transition metal oxide powder can be preferably used as the positive electrode active material. In the present specification, “particle size” means a particle size corresponding to 50% cumulative from the fine particle side in a volume-based particle size distribution measured by particle size distribution measurement based on a general laser diffraction / light scattering method (D ₅₀ particle diameter, also called median diameter).

As the conductive material, one kind or two or more kinds of substances conventionally used in lithium secondary batteries can be used without any particular limitation. For example, it may be one or more selected from various carbon blacks (for example, acetylene black, ketjen black), graphite powder (natural, artificial), carbon fibers (PAN-based, pitch-based) and the like. Or metal fibers (e.g. Al, SUS or the like), conductive metal powder (e.g. Ag, Ni, Cu, etc.), metal oxides (e.g. ZnO, SnO _2, etc.), may be used the surface-coated synthetic fiber such as a metal . Among these, a preferable carbon powder is acetylene black. Although not particularly limited, the proportion of the conductive material in the entire positive electrode mixture layer can be, for example, approximately 0.1% by mass to 15% by mass, and approximately 1% by mass to 10% by mass (more preferably Is preferably 2% by mass to 6% by mass).

  As the binder, one kind or two or more kinds of substances conventionally used in lithium secondary batteries can be used without particular limitation. Typically, various polymer materials can be suitably used. For example, when the positive electrode mixture layer is formed using a solvent-based slurry (a solvent-based composition in which the main component of the dispersion medium is an organic solvent), a polymer material that is dispersed or dissolved in the organic solvent can be preferably used. . Examples of the polymer material include polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), polyethylene oxide (PEO), and the like. Alternatively, when the positive electrode mixture layer is formed using an aqueous slurry, a polymer material that is dissolved or dispersed in water can be preferably used. Examples of such polymer materials include cellulose polymers, fluorine resins, vinyl acetate copolymers, rubbers, and the like. More specifically, carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), styrene butadiene rubber (SBR), acrylic acid-modified SBR resin (SBR latex), and the like. Although it does not specifically limit, the ratio of the binder to the whole positive electrode compound-material layer layer can be 0.1 mass%-10 mass% (preferably 1 mass%-5 mass%), for example.

As the solvent, one kind or two or more kinds of solvents conventionally used in lithium secondary batteries can be used without any particular limitation. Such a solvent is roughly classified into an aqueous solvent and an organic solvent, and examples of the organic solvent include amide, alcohol, ketone, ester, amine, ether, nitrile, cyclic ether, and aromatic hydrocarbon. More specifically, N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide, 2-propanol, ethanol, methanol, acetone, methyl ethyl ketone, methyl propenoate, Cyclohexanone, methyl acetate, ethyl acetate, methyl acrylate, diethyl triamine, N, N-dimethylaminopropylamine, acetonitrile, ethylene oxide, tetrahydrofuran (THF), dioxane, benzene, toluene, ethylbenzene, xylene dimethyl sulfoxide (DMSO), dichloromethane, Examples thereof include trichloromethane and dichloroethane, and N-methyl-2-pyrrolidone (NMP) can be preferably used.
In addition, the aqueous solvent is preferably water or a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use an aqueous solvent in which about 80% by mass or more (more preferably about 90% by mass or more, more preferably about 95% by mass or more) of the aqueous solvent is water. A particularly preferable example is an aqueous solvent (for example, water) substantially consisting of water.

  In addition, various additives (for example, a material that can function as a dispersing agent or an inorganic compound that generates a gas during overcharge) and the like are added to the positive electrode mixture slurry prepared here as necessary. Also good. Examples of the dispersant include a polymer compound having a hydrophobic chain and a hydrophilic group (for example, an alkali salt, typically a sodium salt), an anionic compound having a sulfate, a sulfonate, a phosphate, and the like. And a cationic compound. More specifically, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, butyral, polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphate starch and the like are exemplified. For example, a water-soluble polymer material such as carboxymethyl cellulose is preferably used.

  In addition, as a method for preparing the positive electrode mixture slurry, the positive electrode active material, the conductive material, and the binder may be kneaded at a time, or may be kneaded stepwise in several steps. Preferably, for example, a method may be used in which the conductive material is first dispersed in a solvent, and then the positive electrode active material and the binder are added stepwise. That is, a positive electrode mixture slurry in which a positive electrode active material, a conductive material, and a binder are uniformly dispersed can be obtained by first dispersing a conductive material having relatively poor dispersibility in a solvent. Although not particularly limited, the solid content concentration (NV) of the positive electrode mixture slurry is approximately 50% by mass to 75% by mass (preferably 55% by mass to 65% by mass, more preferably 55% by mass to 60% by mass). ).

Moreover, as a method for forming the positive electrode mixture layer, a method in which an appropriate amount of the positive electrode mixture slurry is applied to one side or both sides of the positive electrode current collector and dried can be preferably employed.
The operation of applying the positive electrode mixture slurry to the positive electrode current collector can be performed in the same manner as in the case of producing a conventional positive electrode for a lithium secondary battery. For example, using a suitable coating apparatus (slit coater, die coater, comma coater, gravure coater, etc.), a predetermined amount of the positive electrode mixture slurry is uniformly formed on one or both surfaces of the positive electrode current collector. It can be made by coating.
Thereafter, the positive electrode mixture layer is dried by an appropriate drying means to remove the solvent contained in the positive electrode mixture slurry. In drying the positive electrode mixture layer, natural drying, hot air, low-humidity air, vacuum, infrared rays, far infrared rays, electron beams, or the like can be used alone or in combination. In a preferred embodiment, the drying temperature is about 200 ° C. or lower (typically 80 ° C. or higher and lower than 200 ° C.). Thus, the positive electrode for lithium secondary batteries disclosed here can be obtained.

After drying of the positive electrode mixture slurry, the thickness and density of the positive electrode mixture layer are appropriately subjected to press treatment (for example, various conventionally known press methods such as a roll press method and a flat plate press method can be employed). Can be adjusted. Note that when the density of the positive electrode mixture layer formed on the positive electrode current collector is extremely low (that is, the amount of the active material in the positive electrode mixture layer is small), the capacity per unit volume decreases. Further, when the density of the positive electrode mixture layer is extremely high, the internal resistance tends to increase particularly during large current charge / discharge or charge / discharge at a low temperature. Therefore, the density of the positive electrode composite material layer may be, for example ^{2.0g / cm 3 ~4.2g / cm 3} ( typically ^{2.5g / cm 3 ~3.2g / cm 3} ).

As the negative electrode of the sealed lithium secondary battery disclosed herein, a negative electrode active material and a binder or the like are mixed as in the positive electrode to form a slurry-like composition (including paste and ink). Hereinafter, a “negative electrode mixture slurry”) is prepared, and the slurry is applied onto a negative electrode current collector to form a negative electrode mixture layer (also referred to as a negative electrode active material layer).
Here, examples of the material for the negative electrode current collector include copper, nickel, titanium, and stainless steel. The form is not particularly limited, and a rod-like body, a plate-like body, a foil-like body, a net-like body, or the like can be used. A battery having a wound electrode body to be described later uses a foil shape. The thickness of the foil-shaped current collector is not particularly limited, but about 5 μm to 50 μm (more preferably 8 μm to 30 μm) can be preferably used in consideration of the capacity density of the battery and the strength of the current collector.

  As the negative electrode active material, one kind or two or more kinds of materials conventionally used in lithium secondary batteries can be used without any particular limitation. For example, particulate graphite powder (carbon particles) including a graphite structure (layered structure) at least partially, oxides such as lithium titanate (LTO), alloys of tin (Sn), silicon (Si) and lithium, and the like Can be mentioned. As the graphite powder, graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), or a combination of these can be used. Among these, graphite can be preferably used. Examples of the graphite include natural graphite (graphite) taken from natural minerals, artificial graphite manufactured from petroleum or coal-based materials, or those obtained by subjecting the graphite to processing such as pulverization or pressing. There may be one or more selected. The proportion of the negative electrode active material in the entire negative electrode mixture layer is not particularly limited, but it is usually appropriately about 50% by mass or more, preferably about 90% by mass to 99% by mass (for example, about 95% by mass to 99% by mass).

  As the binder, an appropriate material can be selected from the polymer materials exemplified as the binder for the positive electrode mixture layer. Examples thereof include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), and the like. What is necessary is just to select suitably the ratio of the binder to the whole negative electrode active material layer according to the kind and quantity of a negative electrode active material, for example, shall be 1 mass%-10 mass% (preferably 2 mass%-5 mass%). Can do. In addition, additives such as various polymer materials (for example, carboxymethyl cellulose (CMC)) that can function as the above-described dispersant, conductive materials, and the like can also be used.

As a method for forming the negative electrode mixture layer, as in the case of the positive electrode described above, a method in which an appropriate amount of the negative electrode mixture slurry is applied to one or both surfaces of the negative electrode current collector and dried can be preferably employed. This drying can be performed under heating as necessary. After drying the negative electrode mixture slurry, the thickness and density of the negative electrode mixture layer are appropriately subjected to press treatment (for example, various conventionally known press methods such as a roll press method and a flat plate press method can be employed). Can be prepared. The density of the negative electrode mixture layer is, for example, 1.1 g / cm ³ or more (typically 1.2 g / cm ³ or more) and 1.5 g / cm ³ or less (typically 1.49 g / cm 2). cm ³ or less).

The electrode body of the sealed lithium secondary battery disclosed herein is characterized by having a structure in which the above-prepared positive electrode and negative electrode are opposed to each other via two or more separators that are independent and overlapped with each other. To do. Then, the electrode body is housed in an appropriate battery case together with an electrolytic solution and an overcharge inhibitor (additive that generates gas when a predetermined battery voltage is exceeded), and a sealed lithium secondary battery is constructed. . The case is provided with a current interruption mechanism (a mechanism capable of interrupting the current in response to an increase in the case internal pressure caused by the generation of the gas when the battery is overcharged) as a safety mechanism.
In the battery described above, an interface exists between the separators / separators by overlapping a plurality of mutually independent separators. For this reason, the movement of the cation radical generated at the positive electrode can be inhibited at the interface, and the amount of the cation radical reaching the negative electrode surface can be suppressed as compared with the conventional case. Therefore, even when the battery environment becomes high temperature and the viscosity of the electrolytic solution decreases, the redox shuttle reaction of the overcharge inhibitor can be suppressed. Moreover, since the decomposition reaction of the overcharge inhibitor is promoted by suppressing the redox shuttle reaction, the amount of gas generated at the time of overcharge can be increased compared to the conventional case. Therefore, the internal pressure increase necessary for operating the current interrupt mechanism can be stably generated at an early stage.
Furthermore, in the sealed lithium secondary battery disclosed herein, the porous heat-resistant layer is preferably disposed in the electrode body so as to be sandwiched between two or more separators independent of each other. Due to the presence of the interface between the porous heat-resistant layer and the separator, the effect of the present invention (ie, inhibiting the movement of cation radicals and promoting the decomposition reaction of the overcharge inhibitor) can be exhibited. it can.

As the separator, various porous sheets similar to those conventionally used for non-aqueous electrolyte secondary batteries can be used. For example, resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, etc. Examples thereof include a porous resin sheet (film) and a non-woven fabric. Such a porous resin sheet may have a single-layer structure, or a structure in which two or more porous resin sheets are laminated (for example, a three-layer structure in which a PP layer is laminated on both sides of a PE layer). Also good.
Here, a separator having a porous heat-resistant layer containing an inorganic filler formed on one surface of the separator can be preferably used. A separator with a porous heat-resistant layer formed may be a commercially available product. For example, a slurry-like composition obtained by mixing an inorganic compound and a binder with an appropriate solvent is applied onto the separator. A porous heat-resistant layer may be formed. Since the separator in which the porous heat-resistant layer is formed has a large specific surface area of the porous heat-resistant layer, the interface between the separators required to inhibit the movement of cation radicals can be further increased. Furthermore, since it is excellent in heat resistance, the application effect of the present invention (that is, an increase in the amount of gas generated under a high temperature environment) can be further exhibited. Furthermore, since the separator formed with the porous heat-resistant layer is excellent in heat resistance, the battery including the separator is destroyed by, for example, deformation of the battery due to impact such as dropping or by nail penetration of a metal object. Even in this case, it is possible to prevent the positive electrode and the negative electrode from coming into contact (internal short circuit) without relying on the separator. For this reason, the heat_generation | fever resulting from this internal short circuit can be suppressed, and reliability (resistance to an overcharge or an internal short circuit) improves further in this battery compared with the past.

Here, the non-conductive (insulating) inorganic compound particles (inorganic filler) are contained in the porous heat-resistant layer. The inorganic compound as the constituent material of the inorganic filler may be one or more selected from oxides, carbides, silicides, nitrides, and the like of metal elements or nonmetal elements. More specifically, aluminum oxide (alumina: Al ₂ O ₃ ), zirconium dioxide (zirconia: ZrO ₂ ), magnesium oxide (magnesia: MgO), silicon oxide (silica: SiO ₂ ), titanium oxide (titania: TiO _2). ), Cerium oxide (ceria: CeO ₂ ), yttrium oxide (yttria: Y ₂ O ₃ ), barium titanate (BaTiO ₃ ) and other oxide-based materials, and cordierite (2MgO · 2Al ₂ O ₃ · 5SiO _2). ), mullite _{(3Al 2 O 3 · 2SiO 2} ), forsterite (2MgO · _SiO 2), steatite (MgO · _SiO 2), sialon _{(Si 3 N 4 · Al 2} O 3), zirconium _(ZrO 2 · SiO _2), ferrite _{(M 2 O · Fe 2 O} 3) composite oxide material such as nitride Ke Containing (silicon _nitride: Si _{3 N} 4), aluminum nitride (aluminum nitride: AlN) nitride material such as silicon carbide (silicon carbide: SiC) carbide-based material such as a hydroxide-based such as hydroxyapatite Examples thereof include elemental materials such as materials, carbon (C), silicon (Si), aluminum (Al), and iron (Fe), or composite materials containing one or more of these.
In the sealed lithium secondary battery disclosed herein, the porous heat-resistant layer preferably contains at least one selected from the group consisting of alumina, magnesia, zirconia, silica, boehmite, and titania. The above compounds have a high melting point and are excellent in heat resistance and chemical stability. Moreover, since it is comparatively cheap, raw material cost can be suppressed.

The D ₅₀ particle size of the inorganic filler can be, for example, about 0.1 μm to 15 μm (preferably about 0.2 μm to 1.5 μm). According to the porous heat-resistant layer formed using ceramic particles having a particle size in the above range, the application effect of the present invention can be more exhibited. The proportion of the inorganic filler contained in the heat-resistant layer is not particularly limited, but is 50% by mass or more (typically 80% by mass or more, for example 90% by mass or more, preferably 95% by mass or more), and 99.8 It can be made into mass% or less (typically 99.5 mass% or less, for example, 99 mass% or less).

  In addition to the inorganic filler, the porous heat-resistant layer can appropriately contain a binder (polymer component) for binding the inorganic filler. As such a binder, it can select from the binder which can be mix | blended with the electrode mixture slurry mentioned above, for example, and can be used. In addition, acrylonitrile-butadiene copolymer rubber (NBR), acrylonitrile-isoprene copolymer rubber (NIR), acrylonitrile-butadiene-isoprene copolymer rubber (NBIR) and other rubbers containing acrylonitrile, acrylic An acrylic polymer having an acid, methacrylic acid, acrylic acid ester or methacrylic acid ester (for example, alkyl ester) as a main copolymerization component can also be used.

  The thickness of the separator is not particularly limited because it can vary depending on the properties and number of separators used. For example, the total thickness of two or more separators is 5 μm to 70 μm (typically 10 μm to 60 μm, for example 10 μm). ˜50 μm). The sealed lithium secondary battery disclosed herein includes a plurality of separators that are independent of each other and stacked. For this reason, there is a possibility that the mobility of lithium ions necessary for charging / discharging is reduced and the resistance (typically, charge transfer resistance) accompanying charging / discharging is increased. However, according to such a configuration, an increase in internal resistance (typically an increase in charge transfer resistance) due to the provision of a plurality of separators can be suppressed, so that high battery performance can be ensured. Therefore, it is possible to increase the reliability of the battery (for example, resistance to overcharge and internal short circuit) while maintaining excellent battery performance.

The properties of the separator (typically a porous resin sheet) vary depending on conditions such as the number of sheets used, and are not particularly limited. For example, the pore diameter is 0.001 to 30 μm (typically 0). The porosity (porosity) of the two or more separators is, for example, approximately 20% to 90% by volume (typically 30% to 20% by volume). About 80 volume%, for example, 35 volume% to 70 volume%) can be used. When the porosity is satisfied, the performance of the present invention (that is, inhibiting the movement of cation radicals at the time of overcharging) and the deterioration of battery performance due to the provision of a plurality of separators (for example, battery capacity) And deterioration of cycle characteristics) can be further suppressed. Therefore, the battery performance and the improvement of the battery reliability (for example, resistance to overcharge and internal short circuit) can be achieved at a high level.
In the present specification, “pore diameter (sometimes referred to as pore diameter)” refers to a value obtained based on a general mercury intrusion measurement unless otherwise specified. For the measurement by the mercury intrusion method, for example, Autopore III 9410 manufactured by Shimadzu Corporation can be used. In the present specification, the “porosity” is obtained by dividing the pore volume (Vb (cm ³ )) obtained by the above measurement by the apparent volume (Va (cm ³ )) and multiplying by 100. Means the calculated value.

  As a battery case, the material and shape which are used for the conventional lithium secondary battery can be used. Examples of the material include relatively light metal materials such as aluminum and steel, and resin materials such as polyphenylene sulfide resin and polyimide resin. Further, the shape (outer shape of the container) is not particularly limited, and may be, for example, a cylindrical shape, a rectangular shape, a rectangular parallelepiped shape, a coin shape, a bag shape, or the like.

As the electrolyte, one kind or two or more kinds similar to the non-aqueous electrolyte used in the conventional lithium secondary battery can be used without any particular limitation. Such a nonaqueous electrolytic solution typically has a composition in which an electrolyte (lithium salt) is contained in a suitable nonaqueous solvent.
As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used. For example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, Examples include 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol, dimethyl ether, ethylene glycol, dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, and γ-butyrolactone. Of these, nonaqueous solvents mainly composed of carbonates are preferably used. For example, the nonaqueous solvent contains one or more carbonates, and the total volume of these carbonates is 60% by volume or more (more preferably 75% by volume or more, and further preferably 90% by volume) of the total volume of the nonaqueous solvent. The non-aqueous electrolyte solution occupying the above and substantially 100% by volume) is preferably used.
Examples of the electrolyte include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiClO _{4 and the} like are exemplified. Of these, LiPF ₆ is preferably used. The concentration of the electrolyte is not particularly limited, but if the concentration of the electrolyte is too low, the amount of lithium ions contained in the electrolytic solution tends to be insufficient, and the ionic conductivity tends to decrease. On the other hand, if the concentration of the supporting electrolyte is too high, the viscosity of the non-aqueous electrolyte solution becomes too high, and the ionic conductivity tends to decrease. For this reason, a nonaqueous electrolytic solution containing an electrolyte at a concentration of about 0.1 mol / L to 5 mol / L (preferably about 0.8 mol / L to 1.5 mol / L) is preferably used.

The overcharge inhibitor to be contained in the electrolyte solution has conventionally been a lithium secondary battery as long as the oxidation potential is equal to or higher than the operating voltage of the lithium secondary battery and decomposes in an overcharged state to generate a large amount of gas. One kind or two or more kinds of substances used in the secondary battery can be used without particular limitation. Examples of such overcharge inhibitors include biphenyl compounds, alkylbiphenyl compounds, cycloalkylbenzene compounds, alkylbenzene compounds, organic phosphorus compounds, fluorine atom-substituted aromatic compounds, carbonate compounds, cyclic carbamate compounds, and alicyclic hydrocarbons. It is done. More specifically, biphenyl (BP), cyclohexylbenzene (CHB), trans-butylcyclohexylbenzene, cyclopentylbenzene, t-butylbenzene, t-aminobenzene, terphenyl, 2-fluorobiphenyl, 3-fluorobiphenyl, 4 -Fluorobiphenyl, 4,4'-difluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, tris- (t-butylphenyl) phosphate, phenyl fluoride, 4-fluorophenyl acetate, diphenyl carbonate, methylphenyl carbonate , Bicterary butyl phenyl carbonate, diphenyl ether, dibenzofuran and the like. For example, in a sealed lithium secondary battery that is fully charged at 4.2 V, those having an oxidation reaction potential of approximately 4.6 V (for example, cyclohexylbenzene (CHB), biphenyl (BP), etc.) can be preferably used. .
In the technology disclosed here, since the reaction efficiency of the overcharge inhibitor is high, the amount of gas necessary for reliably operating the current interrupting device at a high temperature can be reduced with a small amount of overcharge inhibitor compared to the conventional technology. Can be obtained. The amount of the overcharge inhibitor to be used is not particularly limited. However, if an excessive amount is added with an emphasis on reliability, battery performance may be deteriorated (for example, increase in battery resistance or deterioration in cycle characteristics). Therefore, the usage amount of the overcharge inhibitor with respect to 100% by mass of the electrolyte is, for example, about 0.1% by mass or more (typically 0.5% by mass or more, for example, 1% by mass or more), and 7% by mass. (Typically 5% by mass or less, for example 3% by mass or less, preferably 2% by mass or less).

  The current interruption mechanism is not particularly limited as long as the current can be interrupted according to the increase in internal pressure (that is, using the increase in internal pressure as a trigger of operation), and a current interruption mechanism provided in this type of battery is conventionally known. A mechanism similar to any known one can be employed as appropriate. As an example, for example, a configuration shown in FIG. 2 described later can be preferably used. In such a configuration, when the internal pressure of the battery case rises, the member constituting the conductive path from the electrode terminal to the electrode body is deformed, and the conductive path is cut by being separated from the other.

  Although not intended to be particularly limited, as a schematic configuration of a sealed lithium secondary battery according to an embodiment of the present invention, a flatly wound electrode body (wound electrode body) and non-aqueous electrolysis An example of a sealed lithium secondary battery (unit cell) in which liquid is contained in a flat rectangular parallelepiped (box) container is shown in FIGS. In the following drawings, members / parts having the same action are denoted by the same reference numerals, and redundant description may be omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each figure does not reflect the actual dimensional relationship.

FIG. 1 is a perspective view schematically showing the outer shape of a sealed lithium secondary battery 100 according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing a cross-sectional structure taken along line II-II of the sealed lithium secondary battery shown in FIG.
As shown in FIGS. 1 and 2, the sealed lithium secondary battery 100 according to the present embodiment includes a wound electrode body 80 and a hard case (outer container) 50. The hard case 50 includes a flat cuboid (box-shaped) hard case main body 52 having an open upper end, and a lid 54 that closes the opening. On the upper surface of the hard case 50 (that is, the lid 54), a positive electrode terminal 70 that is electrically connected to the positive electrode sheet of the wound electrode body 80 and a negative electrode terminal 72 that is electrically connected to the negative electrode sheet of the electrode body are provided. ing.

  Inside the battery case 50, the long positive electrode sheet 10 and the long negative electrode sheet 20 are two or more long separators 40A (or 42A) and 40B (or 42B) that are independent of each other. The electrode body (winding electrode body) 80 in a flatly wound form is accommodated together with a non-aqueous electrolyte (not shown). Further, the positive electrode sheet 10 is formed such that the positive electrode mixture layer 14 is not provided (or removed) at one end along the longitudinal direction, and the positive electrode current collector 12 is exposed. Similarly, the wound negative electrode sheet 20 is not provided with (or removed from) the negative electrode mixture layer 24 at one end along the longitudinal direction, so that the negative electrode current collector 22 is exposed. Is formed. A positive electrode current collector plate 74 is attached to the exposed end of the positive electrode current collector 12, and a negative electrode current collector plate 76 is attached to the exposed end of the negative electrode current collector 22. Each is electrically connected to the negative terminal 72.

  In addition, a current interrupt mechanism 30 that operates when the internal pressure of the battery case increases is provided inside the battery case 50. The current interruption mechanism 30 only needs to be configured to cut a conductive path (for example, a charging path) from at least one electrode terminal to the electrode body 80 when the internal pressure of the battery case 50 increases, and has a specific shape. It is not limited to. In this embodiment, the current interruption mechanism 30 is provided between the positive electrode terminal 70 fixed to the lid body 54 and the electrode body 80, and reaches from the positive electrode terminal 70 to the electrode body 80 when the internal pressure of the battery case 50 rises. The conductive path is configured to be cut.

  The current interruption mechanism 30 may include a first member 32 and a second member 34, for example. When the internal pressure of the battery case 50 rises, at least one of the first member 32 and the second member 34 is deformed and separated from the other, thereby cutting the conductive path. In this embodiment, the first member 32 is a deformed metal plate, and the second member 34 is a connection metal plate joined to the deformed metal plate 32. The deformed metal plate (first member) 32 has an arch shape in which a central portion is curved downward, and a peripheral portion thereof is connected to the lower surface of the positive electrode terminal 70 via a current collecting lead terminal 35. Further, the tip of the curved portion 33 of the deformed metal plate 32 is joined to the upper surface of the connection metal plate 34. A positive current collector plate 74 is joined to the lower surface (back surface) of the connection metal plate 34, and the positive current collector plate 74 is connected to the positive electrode 10 of the electrode body 80. In this way, a conductive path from the positive electrode terminal 70 to the electrode body 80 is formed.

  The current interrupt mechanism 30 includes an insulating case 38 made of plastic or the like. The insulating case 38 is provided so as to surround the deformed metal plate 32, and hermetically seals the upper surface of the deformed metal plate 32. The internal pressure of the battery case 50 does not act on the upper surface of the hermetically sealed curved portion 33. The insulating case 38 has an opening into which the curved portion 33 of the deformed metal plate 32 is fitted, and the lower surface of the curved portion 33 is exposed from the opening to the inside of the battery case 50. The internal pressure of the battery case 50 acts on the lower surface of the curved portion 33 exposed inside the battery case 50. In the current interrupt mechanism 30 having such a configuration, when the internal pressure of the battery case 50 increases, the internal pressure acts on the lower surface of the curved portion 33 of the deformed metal plate 32, and the curved portion 33 curved downward is pushed upward. The upward push of the curved portion 33 increases as the internal pressure of the battery case 50 increases. When the internal pressure of the battery case 50 exceeds the set pressure, the curved portion 33 is turned upside down and deformed so as to bend upward. Due to the deformation of the curved portion 33, the joint point 36 between the deformed metal plate 32 and the connection metal plate 34 is cut. As a result, the conductive path from the positive electrode terminal 70 to the electrode body 80 is cut, and the overcharge current is cut off.

  The current interrupt mechanism 30 is not limited to the positive terminal 70 side, and may be provided on the negative terminal 72 side. Moreover, the electric current interruption mechanism 30 is not limited to the mechanical cutting | disconnection accompanied with a deformation | transformation of the deformation | transformation metal plate 32 mentioned above. For example, an external circuit that detects the internal pressure of the battery case 50 with a sensor and cuts off the charging current when the internal pressure detected by the sensor exceeds a set pressure may be provided as the current cutoff mechanism.

  FIG. 3 is a diagram schematically showing a long sheet structure (electrode sheet) in a stage before assembling the wound electrode body 80. A positive electrode sheet 10 in which a positive electrode mixture layer 14 is formed along the longitudinal direction on one or both surfaces (typically both surfaces) of a long positive electrode current collector 12, and a long negative electrode current collector 22. Two or more long separators 40 </ b> A (one or two (typically both surfaces)), each having two or more long separators 40 </ b> A (which are stacked on each other independently and overlaid with the negative electrode sheet 20 on which the negative electrode mixture layer 24 is formed along the longitudinal direction. And / or 42A) and 40B (and / or 42B) and wound in the longitudinal direction to produce a wound electrode body. A flat wound electrode body 80 is obtained by squashing and winding the wound electrode body from the side surface direction. Since a battery equipped with a wound electrode body has a high capacity among lithium secondary batteries, it is particularly important to improve reliability (for example, measures against malfunctions). According to the technology disclosed herein, the reliability (for example, resistance to overcharge and internal short circuit) of such a battery can be improved as compared with the conventional technology.

  The sealed lithium secondary battery disclosed herein can be used for various applications, and such a battery is characterized in that the reliability during overcharge is improved even in a high temperature environment. Therefore, the battery is particularly effective when the battery has a high capacity and a high output, and the use and / or leaving environment can be a high temperature. For example, the sealed lithium secondary battery 100 disclosed herein can be suitably used as a power source (drive power source) for a motor mounted on a vehicle 1 such as an automobile as shown in FIG. Although the kind of vehicle 1 is not specifically limited, Typically, a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), and an electric vehicle (EV) are mentioned. Moreover, the sealed lithium secondary battery 100 may be used alone, or may be used in the form of an assembled battery that is connected in series and / or in parallel.

  Hereinafter, as a specific example, whether or not there is a difference in reliability of the battery was evaluated by the method disclosed here (that is, the aspect of the separator). It should be noted that the present invention is not intended to be limited to those shown in the specific examples.

[Construction of sealed lithium secondary battery]
<Example 1>
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder as a positive electrode active material powder, acetylene black (AB) as a conductive material, graphite, and polyvinylidene fluoride (PVdF) as a binder, N-methylpyrrolidone (NMP) was added to a kneader (planetary mixer) so that the mass ratio of the material was about 91: 3: 3: 3, and the solid content concentration (NV) was about 50% by mass. And kneading while preparing the viscosity to prepare a slurry-like composition (positive electrode mixture slurry) for forming the positive electrode mixture layer. This positive electrode mixture slurry was applied to both sides of a long aluminum foil (positive electrode current collector) having a thickness of about 15 μm and dried to form a positive electrode mixture layer. The obtained positive electrode was roll-pressed to produce a sheet-like positive electrode (positive electrode sheet) having an electrode density of about 2.6 g / cm ³ .

Similarly to the above, natural graphite (spherical powder), styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) as the negative electrode active material, the mass ratio of these materials is approximately 98: 1: 1, The mixture was kneaded while adjusting the viscosity with ion-exchanged water so that NV was about 45% by mass to prepare a slurry-like composition (negative electrode mixture slurry) for forming the negative electrode mixture layer. This negative electrode mixture slurry was applied to both sides of a long copper foil (negative electrode current collector) having a thickness of about 10 μm and dried to form a negative electrode mixture layer. The obtained negative electrode was roll-pressed to produce a sheet-like negative electrode (negative electrode sheet) having an electrode density of about 1.4 g / cm ³ .

Next, two types of sealed lithium secondary batteries of a cylindrical type and a laminate sheet type were constructed using the prepared positive electrode sheet and negative electrode sheet.
In the construction of a cylindrical sealed lithium secondary battery, first, the positive electrode sheet and the negative electrode sheet prepared above were separated into separators (here, a three-layer structure in which a PP layer was laminated on both sides of a PE layer (thickness 40 μm 1), and a wound electrode body obtained by crushing and winding the obtained wound electrode body from the side surface. A rotating electrode body was produced. And the positive electrode terminal was joined to the edge part of the positive electrode electrical power collector of this electrode body, and the negative electrode terminal was joined to the edge part of the negative electrode electrical power collector, respectively. Such an electrode body is used as an electrolyte in a nonaqueous electrolytic solution (here, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3: 4: 3). LiPF ₆ was dissolved at a concentration of approximately 1.1 mol / L, and an electrolytic solution containing cyclohexylbenzene (CHB) at a concentration of 2% by mass was used) and contained in a cylindrical battery case. A sensor for detecting internal pressure (internal pressure sensor) and a current interrupting mechanism (CID) were installed in the case. A lid was attached to the opening of the battery case and welded and joined to construct an 18650-type sealed lithium secondary battery (Example 1). The structure of the battery according to Example 1 is schematically shown in FIG.
In the construction of a laminate sheet type sealed lithium secondary battery, first, the positive electrode sheet and the negative electrode sheet prepared above were cut into dimensions of about 45 (mm) × 45 (mm), respectively, and a separator (similar to the above). One electrode having a property and having a three-layer structure in which a PP layer is laminated on both sides of a PE layer was used. And the positive electrode terminal was joined to the edge part of the positive electrode electrical power collector of this electrode body, and the negative electrode terminal was joined to the edge part of the negative electrode electrical power collector, respectively. Such an electrode body is mixed with a non-aqueous electrolyte (here, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of 3: 4: 3, and LiPF as an electrolyte. ₆ was dissolved at a concentration of approximately 1.1 mol / L, and an electrolyte containing 2% by mass of cyclohexylbenzene (CHB) was used.) Type lithium secondary battery (Example 1) was constructed.
Then, the two types of batteries constructed above were subjected to appropriate conditioning at a temperature of 25 ° C. (Here, charging was performed at a constant current of up to 4.1 V at a charging rate of 0.3 C (CC charging). ) And an initial charge / discharge treatment in which the discharge at a constant current of up to 3.0 V at a discharge rate of 0.3 C (CC discharge) was repeated twice.

<Example 2>
In Example 2, two types of sealed lithium secondary batteries (Example 2) were constructed and subjected to conditioning treatment in the same manner as Example 1 except that two separators having a thickness of 20 μm were used in an overlapping manner. The structure of the battery according to Example 2 is schematically shown in FIG.

<Example 3>
In Example 3, a separator (thickness 25 μm, porosity) in which a porous heat-resistant layer (HRL: Heat Resistance Layer) was formed on a base material (PE separator) together with a separator made of PE (one sheet) as the separator. 50% by volume; hereinafter, sometimes simply referred to as “with HRL”.) Two types of sealed lithium secondary batteries (Example 3) were constructed in the same manner as in Example 1 except that a single sheet was used. The conditioning process was performed. The structure of the battery according to Example 3 is schematically shown in FIG.

<Example 4>
In Example 4, two types of sealed lithium secondary batteries (Example 4) were constructed and conditioned in the same manner as in Example 1 except that two sheets with HRL were used instead of the PE separator. Processed. The structure of the battery according to Example 4 is schematically shown in FIG.

[Overcharge test (measurement of gas generation)]
About the laminated sheet type sealed lithium secondary battery (Examples 1 to 4) after the conditioning treatment, the volume of the cell was measured by Archimedes method. Thereafter, the battery was charged at a constant current at a rate of 1 C until it was overcharged (in this example, the SOC was 160%) in an environment of 60 ° C., and the volume of the cell was measured again by the Archimedes method. Then, the volume of the cell after conditioning (B (cm ³ )) is subtracted from the volume of the cell after overcharging (A (cm ³ )), and the amount of gas generated during overcharging (A−B (cm ³⁾ )) Was calculated. The result (A-B (cm ³ / Ah)) obtained by dividing this value by the battery capacity (Ah) is shown in the corresponding part of Table 1.
The Archimedes method is a method in which a measurement object (in this example, a laminated sheet type sealed lithium secondary battery) is immersed in a liquid medium (for example, distilled water or alcohol), and the buoyancy that the measurement object receives is measured. This is a technique for obtaining the volume of the measurement object by measuring.

[Nail penetration test]
The 18650 type sealed lithium secondary battery (Examples 1 to 4) after the conditioning treatment was adjusted to a state where the SOC was 100% (that is, a fully charged state). Then, a thermocouple is attached to the outer surface of each battery case, and under a temperature condition of 20 ° C., an iron nail having a diameter of 3 mm is penetrated near the center of each battery at a speed of 10 mm / sec. Forced internal short circuit. The battery temperature (maximum temperature reached) at this time was measured. The results are shown in the corresponding places in Table 1.

As shown in Table 1, the amount of gas generated at the time of overcharging increased when two sheets were used in combination (Examples 2 to 4), compared to the case where one separator was used (Example 1). The reason for this is that when the number of separators is one (Example 1), the battery environment becomes high temperature (60 ° C. in this case), the viscosity of the electrolyte solution decreases, and the redox shuttle reaction of the overcharge inhibitor is preferential. Therefore, it is considered that the decomposition reaction of the overcharge inhibitor was suppressed and the amount of gas generated was small. On the other hand, when a plurality of mutually independent separators are used in an overlapping manner (Example 2), since there is an interface between the separators / separators, the cation radicals generated at the positive electrode during overcharge at the interface between the separators are present. The migration was inhibited, and the amount of cation radicals reaching the negative electrode surface could be suppressed compared to the conventional case. For this reason, even when the battery environment at the time of overcharge is high and the viscosity of the electrolyte decreases, the decomposition reaction of the overcharge inhibitor is promoted and the amount of gas generated can be increased compared to the conventional case. It is done.
Further, in Example 3 using the separator in which the porous heat-resistant layer is formed on one of the two separators to be superposed, the amount of generated gas is remarkably increased as compared with Example 2 having no porous heat-resistant layer. did. This is probably because the separator having the porous heat-resistant layer has a large specific surface area and can increase the interface between the separators. Furthermore, in Example 4 in which two separators each having a porous heat-resistant layer formed thereon were used, the amount of gas generated was the largest. It is considered that by disposing the porous heat-resistant layer at the interface between the separators, it was possible to further inhibit the movement of cation radicals and promote the decomposition reaction of the overcharge inhibitor.
This result shows the effect of applying the present invention (that is, an increase in the amount of gas generated under a high temperature environment). Furthermore, in the sealed lithium secondary battery, since the reaction efficiency of the overcharge inhibitor is high, it is necessary to reliably operate the current interrupting device even at high temperatures with a smaller amount of overcharge inhibitor than before. It is considered that a large amount of gas can be obtained.

Further, in Examples 3 and 4 using the separator with the porous heat-resistant layer, the maximum temperature reached during the nail penetration test was significantly reduced as compared with Examples 1 and 2 using only the PE separator. This is thought to be because the porous heat-resistant layer having high heat resistance was formed on the separator, so that the separator could not be relied upon even by nail penetration, and the location where the positive electrode and the negative electrode were in contact (that is, the shorted location) did not occur. It is done.
From these results, it was shown that the sealed lithium secondary battery disclosed herein can improve the reliability (resistance to overcharge and internal short circuit) of the battery as compared with the related art.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

1 Automobile (vehicle)
10 Positive electrode sheet (positive electrode)
12 Positive electrode current collector 14 Positive electrode mixture layer 20 Negative electrode sheet (negative electrode)
22 Negative electrode current collector 24 Negative electrode composite material layer 30 Current interruption mechanism 32 Deformed metal plate (first member)
34 Connection metal plate (second member)
38 Insulating cases 40A and 40B Separator sheets 42A and 42B Separator sheet with porous heat-resistant layer 50 Battery case 52 Case body 54 Lid 70 Positive electrode terminal 72 Negative electrode terminal 74 Positive electrode current collector plate 76 Negative electrode current collector plate 80 Winding electrode body 100 Sealing Type lithium secondary battery

Claims (10)

A sealed lithium secondary battery in which an electrode body and an electrolyte are housed in a predetermined battery case,
An additive that generates a gas when a predetermined battery voltage is exceeded, and a current interruption mechanism that operates when the internal pressure of the battery case is increased by the generation of the gas,
The sealed lithium secondary battery is characterized in that the electrode body has a structure in which a positive electrode and a negative electrode face each other through two or more separators that are independent and overlapped with each other. The electrode body is
Two or more long separators independent of each other;
On a long positive electrode current collector, a positive electrode mixture layer having a predetermined width is formed along the longitudinal direction of the current collector, and
On the long negative electrode current collector, a negative electrode mixture layer having a predetermined width is formed along the longitudinal direction of the current collector.
The wound electrode body is formed by laminating the elongated positive electrode and the elongated negative electrode facing each other via the two or more separators and wound in a longitudinal direction. 2. The sealed lithium secondary battery according to 1.   3. The sealed lithium secondary battery according to claim 1, wherein at least one of the separators includes a porous heat-resistant layer containing an inorganic filler on one surface of the separator.   The sealed lithium secondary battery according to claim 3, wherein the two or more separators including the separator having the porous heat-resistant layer are arranged in a state where the porous heat-resistant layer is sandwiched between the separators.   5. The sealed lithium secondary battery according to claim 3, wherein the inorganic filler includes at least one selected from the group consisting of alumina, magnesia, zirconia, silica, boehmite, and titania.   6. The sealed lithium secondary battery according to claim 1, wherein the total thickness of the two or more separators is 5 μm or more and 70 μm or less.   The sealed lithium secondary battery according to any one of claims 1 to 6, wherein the porosity of the whole of the two or more separators is 30% by volume to 80% by volume.   The sealed lithium secondary battery according to any one of claims 1 to 7, comprising cyclohexylbenzene or biphenyl as the additive.   The sealed lithium secondary battery according to any one of claims 1 to 8, wherein an additive amount of the additive is 0.5% by mass or more and 5% by mass or less with respect to 100% by mass of the electrolyte.   A vehicle comprising the sealed lithium secondary battery according to any one of claims 1 to 9 as a driving power source.

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